Green synthesis of various nanoparticle species using spent coffee grounds

Nanotechnology and nanoparticles (NPs) have become a common part of our modern society with uses ranging from medicine and biotechnology to cosmetics, synthetic lubricants, and food safety products. Among these technologies, one emerging NP synthesis method is to utilize food waste products, such as spent coffee grounds (SCGs), adding value and a secondary use for materials which would otherwise have been discarded. SCG synthesis is considered a green synthesis technique which avoids unnecessary exposure to toxic chemicals and reduces harmful waste by replacing caustic precursors with food-derived active compounds. This is in contrast to the many other bottom-up synthesis methods including traditional wet-chemical synthesis, thermal decomposition, hydrothermal, sol-gel, and microemulsion, that utilize hazardous or toxic chemicals and often also produce hazardous or toxic chemical waste. Further, after these syntheses, chemical residues may remain on the surface of these NPs which can affect their biocompatibility, water solubility, end-use function or other attributes. Thus in this study, we seek to expand the understanding and applicability of SCG syntheses of various NP species using SCG extract as the reducing, nucleating, or capping agent in a wet-chemical synthesis. We analyze the impacts of SCGs acquired by hot brew, cold brew, and espresso techniques. Of particular interest are the total antioxidant activity and total caffeoylquinic acid of extracts obtained from SCGs as they play a major role in reduction and nucleation of metal ions during synthesis. Potential new avenues for NP synthesis will also be discussed.